Ink jet printing is an important digital printing method due to its high resolution, flexibility, high speed, and affordability. Such printing is accomplished by ejecting ink from an ink jet print head of the printing apparatus via numerous methods which employ, for example, pressurized nozzles, electrostatic fields, piezo-electric elements, and/or heaters for vapor phase bubble formation.
Many inks currently used in ink jet printers are either water-based or solvent-based. Of these, water-based inks have been widely accepted in the printing industry due to their environmentally friendly attributes. Typical water-based inks consist of little more than pigment or dye in a water/glycol vehicle.
For outdoor applications, where exposed to the elements (e.g., rain), water resistant printable substrates (e.g., polymer films) are desirable. When used with water-based inks, polymer film substrates may be porous and/or have a specialized receptor coating to absorb the ink vehicle and prevent color bleed, both of which features add additional manufacturing steps and associated cost. Further, in many applications employing water-based inks, the printed surface of the substrate must be laminated to a transparent protective cover layer (i.e., an overlaminate) in order to be usable outdoors. Alternatively, the printed image may be made resistant to the elements by means of an additional processing step such as heating in an oven or exposure to ultraviolet (i.e., UV) light. Such additional materials, equipment, and process steps require additional labor and increase the cost of graphic preparation.
The rate at which graphic articles may be prepared depends, at least in part, on the solids content of the ink being used. High solids inks provide high image density without the need for overprinting. Attempts to prepare high solids inks have met with various problems: flocculation of the pigment, clogging of the ink jet nozzle, poor jetting characteristics, and the like.
For at least these reasons, it would be desirable to have a water-based ink, suitable for outdoor applications, that can be directly printed on a wide range of substrates, including non-porous polymeric films, without the need for a specialized ink receptor coating or additional process steps. Further, it would be desirable that such an ink would have a high solids content.